The present invention relates to a method of manufacturing a semiconductor device, and more specifically to a method of reducing a contact resistance between a gate electrode(e.g. a word line in a semiconductor memory device) having a tungsten silicide film at the uppermost and another electrode (e.g. a bit line in a semiconductor memory device) to be formed in the later fabrication process.
In a cell area of semiconductor memory device, the active region(e.g. source/drain region) is coupled to the bit line though a contact hole, while in a peripheral circuit area a word line (or gate electrode) is coupled to the bit line through contact hole. The uppermost part of the word line (or gate electrode) is composed of tungsten silicide film and the bit line is generally composed of a doped polysilicon film(or conductive polysilicon film) or a polycide film. In the peripheral circuit area, a polysilicon bit line is coupled to the tungsten silicide (WSi.sub.x) word line.
When an interlayer insulating film is selectively etched so as to open contact holes, the surface of the tungsten silicide (WSi.sub.x) film is oxidized to generate a tungsten oxide (WO.sub.3) film thereon. Accordingly, in order to reduce the contact resistance with the bit line a washing process should be made, conventionally using HF or fluorine containing solution after the etch for contact hole formation. However, in the peripheral circuit area, the WO.sub.3 film that has been formed during the dry etch of contact hole formation using CF.sub.4 and O.sub.2 gas is not effectively removed so that the contact resistance is undesirably high.
Also, a long-time washing using HF solution is required for completely removing the WO.sub.3 film. However, The long-time washing causes problem in that the BPSG film(or the interlayer insulating film) is undesirably much etched, thereby undesirably enlarging the width of the contact hole. This problem occurs not only in the contact hole formation for exposing the surface of tungsten silicide film but also tungsten film.